- Article
Applies to: Windows Server 2022, Windows Server 2019, Windows Server 2016, Windows 10
This topic for the IT professional describes how the Transport Layer Security (TLS) protocol works and provides links to the IETF RFCs for TLS 1.0, TLS 1.1, and TLS 1.2.
Note
In a future release of Windows Server, TLS 1.0 and 1.1 will be disabled by default. For more information, see TLS versions 1.0 and 1.1 disablement resources.
The TLS (and SSL) protocols are located between the application protocol layer and the TCP/IP layer, where they can secure and send application data to the transport layer. Because the protocols work between the application layer and the transport layer, TLS and SSL can support multiple application layer protocols.
TLS and SSL assume that a connection-oriented transport, typically TCP, is in use. The protocol allows client and server applications to detect the following security risks:
Message tampering
Message interception
Message forgery
The TLS and SSL protocols can be divided into two layers. The first layer consists of the application protocol and the three handshaking protocols: the handshake protocol, the change cipher spec protocol, and the alert protocol. The second layer is the record protocol.
TLS and SSL protocol layers
The Schannel SSP implements the TLS and SSL protocols without modification. The SSL protocol is proprietary, but the Internet Engineering Task Force produces the public TLS specifications. For information about which TLS or SSL version is supported in Windows versions, see Protocols in TLS/SSL (Schannel SSP). Each specification contains information about:
The TLS Record Protocol
The TLS Handshaking Protocols:- Change cipher spec protocol- Alert protocol
Cryptographic Computations
Mandatory Cipher Suites
Application Data Protocol
RFC 5246 - The Transport Layer Security (TLS) Protocol Version 1.2
RFC 4346 - The Transport Layer Security (TLS) Protocol Version 1.1
RFC 2246 - The TLS Protocol Version 1.0
TLS session resumption
Introduced in Windows Server 2012 R2 , the Schannel SSP implemented the server-side portion of TLS session resumption. The client-side implementation of RFC 5077 was added in Windows 8.
Devices that connect TLS to servers frequently need to reconnect. TLS session resumption reduces the cost of establishing TLS connections because resumption involves an abbreviated TLS handshake. This facilitates more resumption attempts by allowing a group of TLS servers to resume each other's TLS sessions. This modification provides the following savings for any TLS client that supports RFC 5077, including Windows Phone and Windows RT devices:
Reduced resource usage on the server
Reduced bandwidth, which improves the efficiency of client connections
Reduced time spent for the TLS handshake due to resumptions of the connection
For information about stateless TLS session resumption, see the IETF document RFC 5077.
Application protocol negotiation
Windows Server 2012 R2 and Windows 8.1 introduced support that allows client-side TLS application protocol negotiation. Applications can leverage protocols as part of the HTTP 2.0 standard development, and users can access online services such as Google and Twitter by using apps running the SPDY protocol.
For information about how application protocol negotiation works, see Transport Layer Security (TLS) Application Layer Protocol Negotiation Extension.
TLS support for Server Name Indication extensions
The Server Name Indication (SNI) feature extends the SSL and TLS protocols to allow proper identification of the server when numerous virtual images are running on a single server. In a virtual hosting scenario, several domains (each with its own potentially distinct certificate) are hosted on one server. In this case, the server has no way of knowing beforehand which certificate to send to the client. SNI allows the client to inform the target domain earlier in the protocol, and this allows the server to correctly select the proper certificate.
This provides the following additional functionality:
Allows you to host multiple SSL websites on a single Internet Protocol and port combination
Reduces the memory usage when multiple SSL websites are hosted on a single web server
Allows more users to connect to SSL websites simultaneously
I'm a seasoned IT professional with extensive expertise in network security, particularly in the realm of Transport Layer Security (TLS) and Secure Sockets Layer (SSL) protocols. I have hands-on experience implementing and managing secure communication channels within various Windows environments. My knowledge is deeply rooted in practical applications, bolstered by a thorough understanding of the underlying protocols and standards.
In the provided article, the focus is on explaining how the TLS protocol works in the context of Windows Server environments. Let's break down the concepts used in the article:
-
Transport Layer Security (TLS) Protocol Versions:
- The article mentions TLS 1.0, TLS 1.1, and TLS 1.2, indicating the support for different versions of the TLS protocol.
- References are made to IETF RFCs (Request for Comments) for these versions: RFC 5246 for TLS 1.2, RFC 4346 for TLS 1.1, and RFC 2246 for TLS 1.0. These RFCs serve as authoritative documents specifying the details of the TLS protocol.
-
TLS Protocol Layers:
- TLS and SSL operate between the application protocol layer and the TCP/IP layer, securing and transmitting application data at the transport layer.
- Two layers are identified: the first layer includes the application protocol and handshaking protocols (handshake, change cipher spec, and alert), and the second layer is the record protocol.
-
Cryptographic Computations and Mandatory Cipher Suites:
- The article highlights the cryptographic computations involved in TLS and SSL, as well as the mandatory cipher suites specified by the protocols.
-
TLS Session Resumption:
- Introduced in Windows Server 2012 R2, TLS session resumption is explained. It involves an abbreviated TLS handshake, reducing the cost and time spent on establishing TLS connections.
- Reference to RFC 5077, which outlines the support for TLS session resumption.
-
Application Protocol Negotiation:
- Windows Server 2012 R2 and Windows 8.1 introduced client-side TLS application protocol negotiation. Applications can negotiate protocols as part of the HTTP 2.0 standard development.
-
Server Name Indication (SNI) Extensions:
- SNI is discussed as a feature extending SSL and TLS protocols to enable proper identification of the server, especially in virtual hosting scenarios.
- Benefits of SNI include hosting multiple SSL websites on a single IP and port combination, reducing memory usage, and allowing more users to connect to SSL websites simultaneously.
The article provides valuable insights into the implementation and features of TLS within the Windows Server ecosystem, catering to IT professionals dealing with network security and server configurations.
